Our technique, histophysiologic gradient culture, is a simple in vitro procedure in which epithelial cells alone or in combination with stroma proliferate as a tissue of many cell layers on a diaphragm of collagen, where both attachemnt and complete nutrient exchange including oxygen take place at the same surface. We will extend our earlier studies on human bladder cancer, normal rat bladder, and rat bladder cancer. As one part of this research we will study certain specific supracellular phenomena that are components of destructive invasion by cancer.